Paloma Faith, who has broken off from her tour to attend, said it was an "amazing" atmosphere and "humbling" to be part of.

"Everyone's very nice and encouraging and there's a good sense of camaraderie between everyone," she said.

"Bob [Geldof] said to me afterwards that my performance was very sad. And I was like, 'Oh no, have I made a mistake?' And he was like, 'No, it's different to what we're used to.'

"The most emotional moment was probably when Bob was giving his speech before we sang. He was saying a few facts about what was going on with the Ebola crisis. I think that injected a lot of raw emotion into the performance."

The singer added: "I feel really good about the fact that as British artists we've all got together regardless of genre or status and I think that's moving."

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Bob Geldof (above, with co-organiser Midge Ure) said the atmosphere "very much reminds me of" the day in 1984 when he first gathered Britain's biggest pop stars to record the first Band Aid single.

It had been "exhausting and embarrassing" calling stars for the new version, he explained.

"It's a song, it's a track, but it's an event and the next stage is to turn it into a phenomenon like it was in the '80s. And the only way to do that is to get people to buy the thing.

"Spare me this free economy. Spare me Spotify and YouTube. There's a donate button on YouTube. Hit the donate button. It's a badge of honour to have this on your phone or on your iPod, or whatever the hell you're using. And don't buy one. Buy several. Give them to your mates."

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U2 frontman Bono has appeared on three of the four versions of Do They Know It's Christmas? to date. "We've been trying to make this event a thing of the past," he said. "We want to make Band Aid history.

"If every country had the values of Great Britain and kept the promises they'd made at these big G8 meetings, we wouldn't have to be standing here. It's not a failure of Great Britain, but outside this country we have a lot of work to do to in getting people to keep their promises.

"I just wish we didn't have to do this. There will come a time when we won't. And it will be great not to see the same old faces." But, referring to the new breed of pop stars involved this time, he added: "What's great about today is it's like Star Trek: The Next Generation."

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The members of One Direction assembled for the occasion. Liam Payne (second left) said the results of the session sounded "really good". He said: "It was so amazing. It was great to be involved in something like this."

Earlier, Niall Horan (left) said: "It's huge to be involved here. Getting invited by Sir Bob is just insane so it's a privilege to be here. Hopefully it gets to number one and raises a lot of money for a really worthy cause."

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Leaving the studio, Olly Murs joked: "I was trying to take Bono's line but he wasn't having it."

The pop star continued: "It was really great to be around everyone. It's a real historic moment for everyone in there, especially us young 'uns." The 2014 recording is "obviously different" to the 1984 original, he said, adding: "But it's still got the message behind the song and that's what we want to get across."

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Chart-topping singer Emeli Sande said she was "excited" to be involved. "It's a real honour so I'm just really excited about today," she said.

"To get the phone call from Bob was a big thing. It's such an important cause for me and my family so it's really important for me to be here."

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Elbow singer Guy Garvey said it was "a real privilege" to be on the record. "It's something I remember so clearly from the first one when I was 10 years old," he said. "I didn't really think I'd ever be invited to do anything like this. But you get the phone call off this gentleman [Bob Geldof] and you go. That's what happens."

The updated lyrics were "excellent" and "in keeping with the standard of the first time", he added. "I've not been able to sleep all night for it going through my head."